The long-range order of pillared interlayered clays (PILCs) after acid activation with 0.05N HCl has been investigated by X-ray diffraction (XRD) methods. The data show that long-range order in PILCs decreases as AlCH-PB = ZrCH-PB » Zr/AlCH-PB - Cr/AlCH-PB (PB - pillared bentonite; MCH = metal chlorohydroxy pillaring agent, where M - Al, Zr or Cr). Apparently, pure oxide clusters are more stable than mixed oxide clusters. Treatment of PILCs with dilute HCI at 25°C is less damaging than at reflux temperature, and calcined PILCs are more stable than air-dried materials. More structural damage occurs with 3M sulfuric acid treatment than with dilute HCI. Treatment with a weak base also causes some degradation of the pillars. 27AI-MAS NMR has been used to study pillared hectorite (PH), as well as other clay systems. The large increase of the observable octahedral aluminum (AI(VI)) resonance seen after pillaring is explained by loss of water from the [Al13O4 (OH) 24 (H2O)12] 7 +(Al13 ) cation. 27A1 spectra of PILCs derived from different pillaring agents and exposed to various heat and acid treatments are remarkably similar.

Soluble polylabdanoids isolated by sequential solvent extraction have been characterized by liquid-state 13C- and 1H NMR and 13C-1H HMQC (heteronuclear correlation) NMR spectroscopy in addition to solid-state NMR and Py–GC–MS techniques. Two Holocene resins originating from Santander, Colombia and Mombasa, Kenya were analyzed. Soluble polymers were isolated by extraction with a 1:1 (v/v) methylene chloride–methanol mixture following sequential extractions with methylene chloride and methanol. The molecular weight of polymer extracts was shown by GPC analyses to exceed that of non-polymeric occluded terpenoids. Py–GC–MS, solid-state 13C CP/MAS and 13C cross-polarization/depolarization NMR spectroscopy results indicated that chemical compositions of soluble polymers isolated from immature resins are highly representative of the structure of corresponding insoluble polymers, i.e. polylabdatrienes. These data provide evidence for cross-linking or cyclization of side-chain olefinic carbons during or shortly after polymerization. Generally, the characterization of soluble resin polymers by liquid-state NMR spectroscopy has proven to be an excellent means for investigating the maturation mechanism of polylabdanoid resinites, and has potential for furthering the application of Class I resinites as geothermal indicators.

This paper reviews earlier NMR studies and provides an overview of present and future applications of NMR imaging for coal structure determination.

NMRI can observe the internal and external physical structural changes of a sample as well as the solvent penetration process without physical handing. Although the spatial resolution achievable in NMRI of coal samples is only 20--40 {mu}m swelling of coal can be measured because a polar solvent expands the coal to almost twice its original volume. NMR can also monitor the change of solvent concentration m a swollen coal (by integrating the peak areas of the NMR spectra), and can also examine solvent mobility (by measuring spin-lattice and spin-spin relaxation times). This paper reports results on application of NMR and NMRI for study of solvent induced-deswelling in an Illinois No. 6 coal.

Pillared bentonites were found to be efficient catalysts for the O-methyl bond cleavage of anisoles (e.g., m-methylanisole, guaiacol, and creosol) under very mild, static conditions (150°C, a few hours, inert atmosphere). The O-methyl bond cleavage led to phenolic products. Gas chromatographymass spectrometry and solid-state 13C nuclear magnetic resonance (NMR) techniques used to probe 13C-labeled anisoles revealed that dealkylation and transalkylation reactions occurred to a large extent, and that conversion was efficient at >95% after two days. Ortho- and para-isomers were observed exclusively, without any evidence of meta-substitution. Volatile products were determined by mass spectrometry to be 13CH3OH and (13CH3)2O. Magic-angle spinning 13C NMR experiments showed that the molecules were fairly mobile in the clay micropores prior to catalysis. After catalysis, cross-polarization NMR showed that molecular motion had decreased markedly. Ultraviolet-visible spectroscopy of the colored complexes suggested some quinone formation. The trend of clay reactivity was found to be: pillared bentonite ≫ acid-washed montmorillonite > untreated bentonite > pillared fluorhectorite ≃ untreated fluorhectorite.

Proton (¹H) nuclear magnetic resonance (NMR) imaging techniques are investigated as a means to nondestructively characterize green-state (unfired) Si{sub 3}N{sub 4} ceramic components. Spectroscopic results indicate that the organic additives used in the injection molding of ceramics behave as soft solids, with broad spectral peak widths (T₂ <0.5 ms) and moderate multicomponent spin-lattice relaxation rates (T{sub 1} ranging from 11 ms to 1 s). Because of the intrinsically different spectral characteristics of the organic additives, conventional-solution NMR imaging techniques cannot be applied to these materials. Hence, the authors developed specialized NMR imaging accessories capable of applying high magnetic field gradients in a back-projection protocol. NMR images were acquired of injection-molded test bars that had been fabricated with different mixing and molding parameters. Organic concentrations determined from the NMR images were correlated with results obtained through destructive testing. The correlation suggests that NMR imaging is a viable technique for quantifying organics in injection-molded green-state ceramics.

Macerals that have been separated from two high-volatile bituminous coals from the Argonne Premium Coal Sample Program are surveyed using chemical and NMR spectroscopic techniques. Quantitative aspects of the method are discussed. Alkylation using {sup 13}C enriched methyl iodide followed by solid {sup 13}C NMR analysis was used to determine the concentrations of acidic OH and CH sites in these macerals. Also, the first successful application of nuclear magnetic resonance imaging (MRI) for spatially mapping chemically distinct regions within a Utah coal has been demonstrated. 15 refs., 5 figs., 2 tabs.

While solid state 13C n.m.r. has made a major contribution to the characterization of coal and other insoluble carbonaceous materials over the past decade, there has been considerable uncertainty concerning the quantitative reliability of the technique. This debate addresses this important topic and comprises six contributions from authors who are recognized experts in n.m.r. characterization of solid fuels. The principal issue discussed is the accuracy of aromaticity measurements on coals by cross-polarization — magic-angle spinning (CP/MAS) 13C n.m.r., together with additional problems posed by high field measurements and spectral editing, and with some discussion of emerging techniques. There is a consensus that significant errors can arise in CP/MAS 13C n.m.r. measurements of aromaticity due to the unfortunate spin-dynamics of coals, which typically result in only ≈50% of the carbon being observed for bituminous coals. There is clear discrimination against aromatic carbon, but differences of opinion exist over the magnitude of the errors (from 2 to 15 mole carbon %) and whether high field (⩾ 50 MHz) measurements are as accurate as those of low field (< 25 MHz) because either sideband suppression or extremely high speed MAS has to be employed to eliminate sidebands. From the evidence presented, it is suggested that a combination of low field, single pulse excitation with long relaxation delays and the use of a suitable reagent to quench paramagnetic centres is the most satisfactory, albeit time consuming, recipe for obtaining reasonably reliable results on unknown samples. An inter-laboratory exercise is being organized by Argonne National Laboratory to check the precision and to further investigate quantitative reliability of 13C n.m.r. measurements on coals from their Premium Coal Sample Bank.

The purpose of this paper is to present the design and test results of a special imaging probe built at Argonne for ceramics characterization. The imaging probe is designed to be used in an 89-mm vertical-bore, 2.35-T superconducting magnet in conjunction with a Bruker CXP-100 spectrometer. The probe must accommodate samples up to 28 mm in diameter, in accordance with our present requirements. The probe includes an RF coil for excitation and detection of the nuclear signals, and a set of gradient coils to create gradient fields with respect to the x, y, and z spatial coordinates. At high field strengths, the gradient coils will generate considerable heat owing to resistive losses; hence, a provision for cooling the probe is included. 7 refs., 10 figs.